Gastroesophageal reflux (GER) has been suggested to play a causal role in a variety of respiratory disorders, including recurrent episodes of pneumonia, asthma, bronchitis, bronchopulmonary dysplasia (BPD), neonatal apnea, and the sudden infant death syndrome. To date, no definitive direct evidence supports this postulate. However, anecdotal report of qualitative improvement of respiratory symptoms following anti-reflux surgery have resulted in increased numbers of patients with respiratory disorders being evaluated for GER, and receiving aggressive medical or surgical management for GER. There is considerable evidence in the literature which suggests that receptors in the esophagus, nasopharynx, larynx, or trachea could mediate changes in control of respiration or mechanics of breathing following GER. Preliminary studies in an animal model which we have developed support the receptor concept, and are the direct stimulus of this proposal. Studies will be performed in the cat to evaluate the short latent changes in respiratory rate, total airway resistence, and lung compliance which follow acid stimulation of the above anatomical locations. The effect of pH, volume, topical anesthesia, and vagotomy on the airway response will be studied. Studies will first be performed in adult animals and then during postnatal development. Investigation of the effect of changes of pulmonary function on esophageal sphincter pressure and esophageal peristalsis will be performed. In concert with animal studies, human studies will be performed to evaluate the incidence of GER and the level of acid reflux in the esophagus in consecutive patients with well defined respiratory disorders. In infants with apnea, measurements of intrasophageal pH in the distal and proximal esophagus will be correlated with simultaneous measurements of respiratory rate, chest wall movement, and nasal air flow. In patients with BPD requiring tracheostomy and mechanical ventilation, airway resistance and lung compliance will be monitored simultaneously with acidification of esophagus with physiologic solutions. Total airway resistence and lung compliance in all applicable studies are calculated by computer from measurement of transpulmonary pressure by intraesophageal or intrapleural catheters, and air flow by pneumotachograph. Data generated by this proposal may establish guidelines for evaluating and managing patients with respiratory disorders associated with GER.